Feedback amplifier as an impedance modulator for a linear power amplifier

ABSTRACT

A power amplifier and power amplification circuit are described herein. An illustrative power amplifier is disclosed to include an input terminal, a drive amplifier connected to the input terminal, and an impedance modulator having a capacitance that is adjusted inversely and proportionately relative to a signal output by the drive amplifier, wherein the impedance modulator provides a feedback loop between an output of the drive amplifier and the input terminal.

FIELD OF THE DISCLOSURE

Example embodiments are generally directed toward power amplifiers andpower amplification circuits.

BACKGROUND

Advanced communication systems, such as 5G beyond 4G, are expected to berealized at wide frequency bandwidths up to 100 MHz to achieve a higherdata transfer rate. However, a power amplifier faces challengingrequirements to support wideband signal modulation due to its highPeak-to-Average Power Ratio (PAPR), which causes distortion of AmplitudeModulation to Amplitude Modulation (AMAM) and Amplitude Modulation toPhase Modulation (AMPM) of an output signal of the power amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

Inventive concepts are described in conjunction with the appendedfigures, which are not necessarily drawn to scale:

FIG. 1 is a block diagram depicting a device in accordance with at leastsome embodiments of the present disclosure;

FIG. 2A is a circuit diagram depicting a power amplifier circuit;

FIG. 2B illustrates behaviors of the power amplifier circuit depicted inFIG. 2A;

FIG. 3A is a circuit diagram depicting a power amplifier circuit inaccordance with at least some embodiments of the present disclosure;

FIG. 3B illustrates behaviors of the power amplifier circuit depicted inFIG. 3A;

FIG. 4 is a circuit diagram depicting additional details of an impedancemodulator circuit in accordance with at least some embodiments of thepresent disclosure;

FIG. 5 is a circuit diagram depicting additional details of an impedancemodulator circuit in accordance with at least some embodiments of thepresent disclosure;

FIG. 6A depicts a simulation result of the input impedance of animpedance modulator circuit in accordance with at least some embodimentsof the present disclosure;

FIG. 6B depicts an input capacitance of a circuit that is modulatedaccording to power in accordance with at least some embodiments of thepresent disclosure;

FIG. 7 depicts a comparison of amplitude modulation to phase modulationwith and without an impedance modulation circuit;

FIG. 8A is a circuit diagram depicting an illustrative differential typefeedback circuit in accordance with at least some embodiments of thepresent disclosure;

FIG. 8B is a circuit diagram depicting an alternative illustrativedifferential type feedback circuit in accordance with at least someembodiments of the present disclosure; and

FIG. 9 is a circuit diagram depicting additional details of an impedancemodulator circuit in accordance with at least some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

One technique to support the wideband signal, which has a high PAPR, isto employ an Average Power Tracking (APT), where bias voltage isadjusted according to average power. An issue associated with using APTis that a linearity of the PA and the nonlinearity of a HeterojunctionBipolar Transistor (HBT) within the PA makes AMAM distortion and theAMPM distortion at high power region, close to saturated power.

Conventionally, with the APT technique, the AMAM distortion is fairlyeasily improved by some methods which are controlling gain profile.However, the typical way to compensate the AMPM distortion is boostingthe base voltage, Vbe, of the HBT. This can be done by increasing thebias voltage, but such an action leads to very poor efficiency which isa main problem of the APT technique for the high PAPR 5G signal.

The above-noted shortcomings associated with advanced communicationsystems and power amplifiers used in the same will be addressed byembodiments of the present disclosure.

Specifically, embodiments of the present disclosure provide a poweramplifier that includes a pre-distortion circuit which corrects the AMPMdistortion by distorting phase at the input terminal proportionately andin an opposite direction to that of original distortion.

In other words, the phase at input terminal may be configured todecrease as the power increases because a shunt capacitance can beprovided at the input terminal increases as the power increases.Therefore, the phase of a driver stage may be opposite to that of a mainstage and the AMPM distortion of the total PA becomes nearly zero.

The ensuing description provides embodiments only, and is not intendedto limit the scope, applicability, or configuration of the claims.Rather, the ensuing description will provide those skilled in the artwith an enabling description for implementing the described embodiments.It being understood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope ofthe appended claims.

Various aspects of example embodiments will be described herein withreference to drawings that are schematic illustrations of idealizedconfigurations. As such, variations from the shapes of the illustrationsas a result, for example, manufacturing techniques and/or tolerances,are to be expected. Thus, the various aspects of example embodimentspresented throughout this document should not be construed as limited tothe particular shapes of elements (e.g., regions, layers, sections,substrates, etc.) illustrated and described herein but are to includedeviations in shapes that result, for example, from manufacturing. Byway of example, an element illustrated or described as a rectangle mayhave rounded or curved features and/or a gradient concentration at itsedges rather than a discrete change from one element to another. Thus,the elements illustrated in the drawings are schematic in nature andtheir shapes are not intended to illustrate the precise shape of anelement and are not intended to limit the scope of example embodiments.

The phrases “at least one,” “one or more,” “or,” and “and/or” areopen-ended expressions that are both conjunctive and disjunctive inoperation. For example, each of the expressions “at least one of A, Band C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “oneor more of A, B, or C,” “A, B, and/or C,” and “A, B, or C” means Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, or A, B and C together.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis disclosure.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “include,”“includes,” “including,” “comprise,” “comprises,” and/or “comprising,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The term “and/or” includes any and all combinations of one ormore of the associated listed items.

Referring initially to FIG. 1, additional details of a device 100 havinga power amplifier 104 will be described in accordance with at least someembodiments of the present disclosure. The device 100 may include anytype of fixed or mobile communication device that is configured forwireless communications. Specifically, the device 100 may correspond toa smart phone, laptop, wearable device, tablet, mobile phone, or thelike that is configured to communicate using 5G frequency bands (e.g.,frequencies bands between 3 GHz and 100 GHz).

The device 100 may include a number of different components, which arenot depicted. The power amplifier 104 that is shown as being included inthe device 100 may correspond to a sub-system of a larger communicationmodule or Integrated Circuit (IC) chip provided in the device 100. Insome embodiments, the power amplifier 104 may be realized within awireless communication module that is connected to a larger PrintedCircuit Board (PCB) in the device 100. The wireless communication moduleand the power amplifier 104 may enable the device 100 to send andreceive voice, video, text, and other data within defined frequencybands.

In some embodiments, the power amplifier 104 may include an inputterminal 108, a drive amplifier 112, a main stage amplifier 116, and anoutput terminal 120. The power amplifier 104 may be considered a linearpower amplifier because the driver amplifier 112 and main stageamplifier 116 are connected in a linear fashion between the inputterminal 108 and the output terminal 120.

The power amplifier 104 is further shown to include an impedancemodulator 124 and a controller 148 that is configured to controloperations of the impedance modulator 124. In some embodiments, thecontroller 148 may correspond to a CMOS controller and may provide abias voltage to the impedance modulator 124 as part of controllingoperations of the impedance modulator 124. In some embodiments, thecontroller 148 may be configured to adjust the bias voltage provided tothe impedance modulator 124 based on a temperature measured in proximityto the controller 148 (e.g., with a temperature sensor provided on ornear the controller 148 or within a predetermined proximity of thecontroller 148). In some embodiments, the controller 148 may beconfigured to the control the bias voltage based on a frequency at whichinput signals are received at the input terminal 108. Said another way,if the input terminal 108 is receiving signals within a particularfrequency band, then the controller 148 may be configured tospecifically adjust the bias voltage provided to the impedance modulator124 based on the particular frequency band. The frequency of the signalreceived at the input terminal 108 may be variable so, in someembodiments, the controller 148 may be configured to dynamically adjustthe bias voltage provided to the impedance modulator 124 based onchanges of frequency realized at the input terminal 108. Said anotherway, the frequency at the input terminal 108 may be variable and thecontroller 148 may be configured to detect such frequency changes andadjust the bias voltage provided to the impedance modulator 124.

The impedance modulator 124 is shown to provide a feedback between anoutput of the drive amplifier 112 and the input terminal 108. In someembodiments, the impedance modulator 124 provided as part of apre-distortion circuit that corrects AMPM distortion by distorting phaseat the input terminal 108 in a direction opposite to original distortionprovided by an input signal received at the input terminal 108. Theimpedance modulator 124 may provide a variable capacitance at the inputterminal 108 that is adjusted inversely and proportionately relative tothe signal output by the driver amplifier 112.

In some embodiments, the impedance modulator 124 may include a detectingamplifier 128, an inverting amplifier 132, a capacitor 136, one or moreresistors 140, and a switch 144. As will be discussed in further detailherein, these components of the impedance modulator 124 may beconfigured to enable functionality of the impedance modulator 124, butnot all of the components are required in every instance of theimpedance modulator 124. In some embodiments, the detecting amplifier128 may be configured to receive the signal output by the driveamplifier 112 and amplify the signal output by the drive amplifier 112.The inverting amplifier 132 may be configured to receive the output fromthe detecting amplifier 128 (e.g., the amplified version of the signaloutput by the drive amplifier 112) and produce a modulated output basedon the signal received from the detecting amplifier 128. The output ofthe inverting amplifier 132 may be provided to a capacitor 136 that isshunt connected at the input terminal 108. Outputs of the invertingamplifier 132 provided to the capacitor 136 may cause a capacitance ofthe capacitor 136 provided to the input terminal 108 to be adjustedinversely and proportionately relative to the signal output by the driveamplifier 112. In some embodiments, a capacitance of the capacitor 136may be modulated based at least in part on a power input at the inputterminal 108. The resistor 140 may be connected between a ground and anoutput of the inverting amplifier 132.

Additional details of the various components of the power amplifier 104will now be described with reference to FIGS. 2A through 9. It should beappreciated that a power amplifier 104 may include some or all of thefeatures depicted and described herein, but a power amplifier 104 doesnot necessarily need to include all of the features depicted anddescribed herein.

FIGS. 2A and 2B illustrate a circuit 200 and possible outputs of acircuit 200 that does not include an impedance modulator 124. Thecircuit 200 does illustrate an input terminal 204 and output terminal208 with a drive amplifier 212 and main stage amplifier 216 connectedtherebetween. In this particular circuit 200, the drive amplifier 212and main stage amplifier 216 provide two distinct signal amplificationstages. The driver stage provided by the drive amplifier 212 maycorrespond to a sub-gain block and the main stage amplifier 216 mayprovide a main amplification stage for the power amplifier 104.

As shown in FIG. 2B, each active stage distorts the AMPM and the amountof distortion increases as power increases. Moreover, the total AMPM ofthe circuit 200 (e.g., a power amplifier 104 without an impedancemodulator 124) may correspond to a sum of the distortion of both stages.Specifically, FIG. 2B illustrates the drive amplifier phase modulationas a function of output power 220 and the main stage amplifier phasemodulation as a function of output power 224. The total AMPM 228 of thecircuit 200 is shown to have a larger AMPM than either amplificationstage because both amplification stages distort the AMPM in a similarmanner.

FIGS. 3A and 3B illustrate a circuit 300 and possible outputs of acircuit 300 that does include a variable capacitor 304. Specifically,the variable capacitor 304 may be provided by way of an impedancemodulator 124 as depicted and described herein.

In some embodiments, the capacitance of the variable capacitor 304 maybe configured to increase according to output power. This increase incapacitance may result in phase compensation as shown in FIG. 3B.Specifically, the drive amplifier phase modulation as a function ofoutput power 308 may decrease while the main stage amplifier phasemodulation as a function of output power 312 may increase. Thedistortion of the combined output 316 of the circuit 300 (e.g., thesummation of the phase modulation 308 and phase modulation 312)effectively becomes zero. In other words, the variable capacitor 304 maycorrect the AMPM distortion of the circuit 300 by distorting the phaseat the input terminal 204 in the opposite direction to that of originaldistortion. Thus, the phase modulation 308 at the input terminal 204 maydecrease as the power increases since the shunt capacitance provided bythe variable capacitor 304 to the input terminal 204 increases as thepower decreases. This causes the phase modulation of the drive stageamplifier 308 to be opposite to that of the phase modulation of the mainstage amplifier 312, which drives the total combined phase modulation316 of the circuit 300 to approach zero.

Additional details of circuits which may be used for the impedancemodulator 124 will now be described in accordance with at least someembodiments of the present disclosure. Referring initially to FIG. 4,details of a circuit 400 will be described in accordance with at leastsome embodiments of the present disclosure. The circuit 400 maycorrespond to a portion of circuit 300 where the variable capacitor 304is provided by the impedance modulator 408. The impedance modulator 408may be similar or identical to impedance modulator 124 and the impedancemodulator 408 may provide a capacitance to the input terminal 204 thatis adjusted inversely and proportionately relative to a signal output bythe amplifier 404.

In some embodiments, the amplifier 404 may correspond to an example of adrive amplifier 112, 212. The impedance modulator 408 is shown as beingconnected directly to the amplifier 404, but the impedance modulator408, in some embodiments, may be connected to the output 402 of theamplifier 404. The signal output by the amplifier 404 may be provided asan input to the impedance modulator 408, which initially receives thesignal at the detecting amplifier 412. In some embodiments, thedetecting amplifier 412 may be similar or identical to the detectingamplifier 128. The output 402 may also correspond to an input of themain stage amplifier 116, 216.

The detecting amplifier 412 may be configured to receive/detect thesignal output by the amplifier 404 and amplify the signal output by theamplifier 404 into an amplified signal. The output of the detectingamplifier 412 (e.g., the amplified version of the signal output by theamplifier 404) may be provided directly to the inverting amplifier 416,which modulates the signal received from the detecting amplifier 412.The inverting amplifier 416 may be similar or identical to invertingamplifier 132.

The output of the inverting amplifier 416 may be provided between acapacitor 420 and resistor 424 that is connected to ground GND. Itshould be appreciated that ground GND may correspond to an absoluteground (e.g., electrical potential equal to zero) or a relative ground.The potential at ground GND may float or be fixed.

The CMOS controller 428 is shown to provide a control signal to theimpedance modulator 408. The CMOS controller 428 may correspond to oneexample of a controller 148. In some embodiments, the CMOS controller428 may comprise digital circuit elements (e.g., transistors) thatenable the CMOS controller 428 to generate and adjust a bias voltageprovided to the impedance modulator 408. The CMOS controller 428 mayadjust the bias voltage based on a measured frequency of a signalreceived at the input terminal 204, based on an expected frequency of asignal received at the input terminal 204, based on a temperature on oraround the CMOS controller 428, based on a temperature on or around theimpedance modulator 408, or combinations thereof.

Referring now to FIG. 5, additional details of the impedance modulator408 will be described in accordance with at least some embodiments ofthe present disclosure. Specifically, FIG. 5 illustrates a circuit 500in which the bias voltage is shown between the detecting amplifier 532and the inverting amplifier 528. It should be appreciated that thedetecting amplifier 532 may be similar or identical to any otherdetecting amplifier (e.g., amplifiers 128, 412) depicted and describedherein. Likewise, it should be appreciated that the inverting amplifier528 may be similar or identical to another other inverting amplifier(e.g., amplifiers 132, 416) depicted and described herein.

The circuit 500 illustrates an input terminal 504, which may be similarto input terminal 204. Circuit 500 also illustrates a capacitor 508 andresistor 512, which may be similar or identical to capacitors 136, 420and resistors 140, 424, respectively. The detecting amplifier 532 isshown to receive an impedance modulator input 544, which may correspondto an output of the drive amplifier 212. The detecting amplifier 532includes at least a first transistor X1. The inverting amplifier 528 isshown to be connected to the detecting amplifier 544 through resistor536 and one or more bias resistors 520, 524. These resistors 520, 524,536 may correspond to actual resistors and/or an inherent resistance ofa conductive wire or trace positioned between the detecting amplifier532 and inverting amplifier 528. In the detected embodiment, theinverting amplifier 528 may include transistor X2 and transistor 540that are connected to one another.

The transistor X1 of the detecting amplifier 532 is shown to have thebase connected to input 544, the emitter connected to ground, and thecollector connected to the base of transistor X2 provided in theinverting amplifier 528. The emitter of the transistor X2 may beconnected directly to the collector of transistor 540 while thecollector of the transistor X2 may be connected to the output of theinverting amplifier 528, which may be connected to VIM through resistor516. In some embodiments, the bias voltage provided by the controller(e.g., controller 148 or CMOS controller 428) may be on the order of 3V.It should be appreciated, however, that the bias voltage may varyanywhere between 1V and 4V without departing from the scope of thepresent disclosure.

An operation theory of the power dependent variable capacitor 304 may beprovided by the circuitry connected to the capacitor 508. Additionaldetails of the operation of the circuit 500 will now be described inaccordance with at least some embodiments of the present disclosure andwith reference to the following equations:

$\begin{matrix}{{\frac{I_{IM}}{V_{IN} - V_{IM}} = {\frac{I_{IM}}{V_{IN}\left( {1 - A} \right)} = {j\omega C}_{IM}}},{V_{IM} = {A \times V_{IN}}}} & \left( {{Equation}\mspace{14mu} 1} \right) \\{{1 - A} = {k_{1} - {jk}_{2}}} & \left( {{Equation}\mspace{14mu} 2} \right) \\{\frac{I_{IM}}{V_{IN}} = {{{j\omega C}_{IM}\left( {1 - A} \right)} = {{{j\omega C}_{IM}k_{1}} + {{\omega C}_{IM}k_{2}}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

In particular, the admittance in terms of a capacitor 508 C_(IM), VIN,and VIM, which are the voltage at each node of the capacitor 508respectively, and the current through the capacitor 508, IIM. The VIMcan be expressed in terms of a voltage gain, A, and the input voltage,VIN. And the term (1-A) in (Equation 1) can be expressed as a complexnumber in terms of coefficients k₁ and k₂ as (Equation 2). By (Equation1 and Equation 2), the input admittance of the impedance modulatorcircuit 500 can be expressed as (Equation 3). The imaginary part of theadmittance in (Equation 3) is a reactance of the circuit 500 which isproportional to the coefficient k₂ which is related to the voltage VIM.As a result, the input capacitance (C_(IM)) of the circuit 500 variesaccording to the power since the VIM changes according to the power. Theeffectively means that the circuit 500 is configured to provide avariable capacitance in accordance with at least some embodiments of thepresent disclosure.

FIGS. 6A and 6B illustrate operational capabilities of the circuit 500or similar circuits depicted and described herein. Specifically, FIG. 6Aillustrates the input impedance 604 of the impedance modulator 408 orcircuit 500. At a low power region, the impedance 604 is at a high andpure resistive region. The impedance 604 moves to capacitive region in acertain power region, and the resistance of the impedance 604 decreasesat the same time. Also, the reactance, which is arranged in the(Equation 3), can be calculated as a capacitance. FIG. 6B illustratesthe input capacitance 608 of the impedance modulator 408 or circuit 500and shows that the input capacitance of the circuit 500 can be modulatedaccording to the power.

The result of a pre-distorted AMPM of a power amplifier employingembodiments of the present disclosure is plotted in FIG. 7.Specifically, FIG. 7 illustrates the AMPM for the drive amplificationstage 704, the AMPM for the main amplification stage 708, and the totalAMPM for the power amplifier 712. Each chart illustrates a circuitperformance or behavior for a traditional power amplifier 716 that doesnot employ an impedance modulator 408 or variable capacitance next to acircuit performance or behavior for a power amplifier 720 that doesemploy an impedance modulator 408 or variable capacitance in accordancewith embodiments of the present disclosure. As can be seen in FIG. 7,the AMPM for the drive amplification stage 704 is significantlydifferent for the traditional power amplifier 716 as compared to a poweramplifier 720 having improvement described herein. Thus, the total AMPMfor the power amplifier 712 will behave far better if the poweramplifier includes an impedance modulator 408 or variable capacitance asdescribed herein.

Conventionally, analog circuitry has an inherent problem ofcharacteristic variation over temperature. On the other hand,embodiments of the present disclosure can enable a power amplifier andcircuits provided therein to remain insensitive to the temperaturechange since the control voltage of this circuitry is offered from aCMOS controller 428 which can control the voltage level according to thetemperature. Consequently, this circuitry can be biased at each optimumvoltage over different temperatures. Also, the controllability of thebias voltage has an advantage of wide-bandwidth characteristic by meansof applying an optimum bias for each frequency or frequency band.

FIGS. 8A and 8B illustrate a feedback circuit 800, 836 with the poweramplifier which is a differential type. With the differential poweramplifier 812, embodiments described herein provide an advantage indesign freedom since there are two signal paths. In other words, designand layout of an IC chip can be easily modified by the convenience ofdesigners since only one of both signal paths is need to be connected tothe impedance modulator 828 as plotted in FIGS. 8A and 8B. Morespecifically, the circuit 800 may include the differential poweramplifier 812 connected between an input terminal 804 and outputterminal 808. The input terminal 804 may be similar or identical toother input terminals (e.g., terminal 108, 204, 504, etc.) depicted anddescribed herein and the output terminal 808 may be similar or identicalto other output terminals (e.g., terminal 120, 208, etc.) depicted anddescribed herein.

The differential power amplifier 812 may still include a drive amplifier816, which may be similar or identical to drive amplifier 112, 212, or404. The differential power amplifier 812 is also shown to include apositive main amplifier 820 and a negative main amplifier 824 that arecoupled to the output terminal 808 via an inductive coupling 828 ortransformer. As shown in FIG. 8A, the impedance modulator 828 may beconnected directly to the negative main amplifier 824 and the CMOScontroller 832 may operate the impedance modulator 828 as describedherein. Alternatively, as shown in FIG. 8B, the impedance modulator 828may be connected directly to the positive main amplifier 820 and theCMOS controller 832 may operate the impedance modulator 828 as describedherein. In other words, the behavior of the impedance modulator 828 andCMOS controller 832 may be maintained as if the power amplifier were alinear power amplifier without departing from the scope of the presentdisclosure. Specifically, the impedance modulator 828 may be similar oridentical to any other impedance modulator depicted and described herein(e.g., impedance modulator 124, 408, and circuit 500). Similarly, theCMOS controller 832 may be similar or identical to controller 148 or theCMOS controller 428 without departing from the scope of the presentdisclosure.

Furthermore, the circuitry of the present disclosure can be configuredto be turned off or on by using a switch 904 as depicted in FIG. 9,which illustrates a circuit 900 having similarities to circuit 400, butwith the additional functionality provided by switch 904. It should beappreciated that the duplicative details of circuit 900 alreadydescribed in connection with circuit 400 will not be re-described forconvenience of discussion. The impedance modulator 408 may include oneor many circuit components that enable an on/off switch 904 as shown inFIG. 9. In some embodiments, the switch 904 may be provided as aswitching transistor. It may be useful to employ a switch 904 since thepower amplifier may be configured to operate in many different modes(e.g., low power mode, high power mode, APT mode, Envelope Trackingmode, etc.) to support complex communication schemes. The switch 904 mayprove particularly useful at the low power mode which may present arequirement of minimum current since active components of circuitrywould add extra current on the total current flowing through the poweramplifier. Thus, the switch 904 may be moveable between an on state andoff state to selectively enable and disable operation of the impedancemodulator 408 within circuit 900. In some embodiments, the state of theswitch 904 may be controlled by the CMOS controller 428.

At least one example embodiment is directed to a power amplifier thatincludes: an input terminal; a drive amplifier connected to the inputterminal; and an impedance modulator having a capacitance that isadjusted inversely and proportionately relative to a signal output bythe drive amplifier, where the impedance modulator provides a feedbackloop between an output of the drive amplifier and the input terminal.

According to one aspect, the power amplifier may further include a mainstage amplifier having an input connected directly to the output of thedrive amplifier, where the signal output by the drive amplifier andreceived at the impedance modulator is also provided to the input of themain stage amplifier.

In some embodiments, the impedance modulator further includes: adetecting amplifier that receives the signal output by the driveamplifier and that amplifies the signal output by the drive amplifier;and an inverting amplifier that receives an output of the detectingamplifier and that modulates the output of the detecting amplifier.

In some embodiments, the impedance modulator further includes: acapacitor that is shunt connected at the input terminal; and a resistorconnected between ground and an output of the inverting amplifier,wherein the output of the inverting amplifier is provided to thecapacitor.

In some embodiments, the power amplifier further includes a controllerthat provides a bias voltage to the impedance modulator. According toone aspect, the controller comprises a CMOS controller and the CMOScontroller is configured to control the bias voltage based on afrequency at which input signals are received at the input terminal. Insome embodiments, the frequency is variable.

According to one aspect, the capacitance is modulated based at least inpart on a power input at the input terminal.

According to one aspect, the impedance modulator is provided as part ofa pre-distortion circuit that corrects amplitude modulation to phasemodulation (AMPM) distortion by distorting phase at the input terminalin a direction opposite to original distortion provided by an inputsignal received at the input terminal.

Another example embodiment provides a power amplification circuit thatincludes: an input terminal; an output terminal; a drive amplifierhaving an input connected to the input terminal; a main stage amplifierhaving an input connected to an output of the drive amplifier and havingan output connected to the output terminal; and an impedance modulatorhaving a capacitance that is adjusted inversely and proportionatelyrelative to a signal output by the drive amplifier, where the impedancemodulator is connected between the drive amplifier and main stageamplifier and further provides a feedback loop between the output of thedrive amplifier and the input terminal.

According to one aspect, the impedance modulator further includes: adetecting amplifier that receives the signal output by the driveamplifier and that amplifies the signal output by the drive amplifier;and an inverting amplifier that receives an output of the detectingamplifier and that modulates the output of the detecting amplifier.

According to one aspect, the impedance modulator further includes: acapacitor that is shunt connected at the input terminal; and a resistorconnected between ground and an output of the inverting amplifier, wherethe output of the inverting amplifier is provided to the capacitor.

According to one aspect, the power amplification circuit may furtherinclude a switching transistor configured to selectively turn theimpedance modulator on or off depending upon a state of the switchingtransistor. In some embodiments, the switching transistor is connectedbetween the inverting amplifier and the capacitor.

According to one aspect, the power amplification circuit furtherincludes a controller that provides a bias voltage to the impedancemodulator. In some embodiments, the controller comprises a CMOScontroller and the CMOS controller is configured to adjust the biasvoltage based on a temperature measured in proximity to the CMOScontroller.

According to one aspect of the present disclosure, the impedancemodulator is provided as part of a pre-distortion circuit that correctsamplitude modulation to phase modulation (AMPM) distortion by distortingphase at the input terminal in a direction opposite to originaldistortion provided by an input signal received at the input terminal.

Another example embodiment provides a circuit that includes: a detectingamplifier that receives a signal output by a drive amplifier and thatamplifies the signal output by the drive amplifier; an invertingamplifier that receives an output of the detecting amplifier and thatmodulates the output of the detecting amplifier; and a capacitor havinga capacitance that is adjusted inversely relative to the signal outputby the drive amplifier, where the capacitor is shunt connected to aninput of the drive amplifier.

According to one aspect, the circuit further includes: a main stageamplifier having an input connected to an output of the drive amplifierand having an output connected to an output terminal; and a CMOScontroller configured to control a bias voltage provided between theinverting amplifier and the detecting amplifier based on a frequency atwhich input signals are received at the input of the drive amplifier.

According to one aspect, the circuit further includes: a switchconnected between the capacitor and inverting amplifier and thatselectively enables or disables current from flowing between thecapacitor and the inverting amplifier.

Specific details were given in the description to provide a thoroughunderstanding of example embodiments. However, it will be understood byone of ordinary skill in the art that example embodiments may bepracticed without these specific details. In other instances, well-knowncircuits, processes, algorithms, structures, and techniques may be shownwithout unnecessary detail in order to avoid obscuring exampleembodiments.

While illustrative embodiments have been described in detail herein, itis to be understood that inventive concepts may be otherwise variouslyembodied and employed, and that the appended claims are intended to beconstrued to include such variations, except as limited by the priorart.

What is claimed is:
 1. A power amplifier, comprising: an input terminal;a drive amplifier connected to the input terminal; an impedancemodulator having a capacitance that is adjusted inversely andproportionately relative to a signal output by the drive amplifier,wherein the impedance modulator provides a feedback loop between anoutput of the drive amplifier and the input terminal; and a controllerthat provides a bias voltage to the impedance modulator.
 2. The poweramplifier of claim 1, further comprising: a main stage amplifier havingan input connected directly to the output of the drive amplifier,wherein the signal output by the drive amplifier and received at theimpedance modulator is also provided to the input of the main stageamplifier.
 3. The power amplifier of claim 2, wherein the impedancemodulator further comprises: a detecting amplifier that receives thesignal output by the drive amplifier and that amplifies the signaloutput by the drive amplifier; and an inverting amplifier that receivesan output of the detecting amplifier and that modulates the output ofthe detecting amplifier.
 4. The power amplifier of claim 3, wherein theimpedance modulator further comprises: a capacitor that is shuntconnected at the input terminal; and a resistor connected between groundand an output of the inverting amplifier, wherein the output of theinverting amplifier is provided to the capacitor.
 5. The power amplifierof claim 1 wherein the controller comprises a CMOS controller andwherein the CMOS controller is configured to control the bias voltagebased on a frequency at which input signals are received at the inputterminal.
 6. The power amplifier of claim 5, wherein the frequency isvariable.
 7. The power amplifier of claim 1, wherein the capacitance ismodulated based at least in part on a power input at the input terminal.8. The power amplifier of claim 1, wherein the impedance modulator isprovided as part of a pre-distortion circuit that corrects amplitudemodulation to phase modulation (AMPM) distortion by distorting phase atthe input terminal in a direction opposite to original distortionprovided by an input signal received at the input terminal.
 9. A poweramplification circuit, comprising: an input terminal; an outputterminal; a drive amplifier having an input connected to the inputterminal; a main stage amplifier having an input connected to an outputof the drive amplifier and having an output connected to the outputterminal; an impedance modulator having a capacitance that is adjustedinversely and proportionately relative to a signal output by the driveamplifier, wherein the impedance modulator is connected between thedrive amplifier and the main stage amplifier and further provides afeedback loop between the output of the drive amplifier and the inputterminal; and a controller that provides a bias voltage to the impedancemodulator.
 10. The power amplification circuit of claim 9, wherein theimpedance modulator further comprises: a detecting amplifier thatreceives the signal output by the drive amplifier and that amplifies thesignal output by the drive amplifier; and an inverting amplifier thatreceives an output of the detecting amplifier and that modulates theoutput of the detecting amplifier.
 11. The power amplification circuitof claim 10, wherein the impedance modulator further comprises: acapacitor that is shunt connected at the input terminal; and a resistorconnected between ground and an output of the inverting amplifier,wherein the output of the inverting amplifier is provided to thecapacitor.
 12. The power amplification circuit of claim 11, furthercomprising: a switching transistor configured to selectively turn theimpedance modulator on or off depending upon a state of the switchingtransistor.
 13. The power amplification circuit of claim 12, wherein theswitching transistor is connected between the inverting amplifier andthe capacitor.
 14. The power amplification circuit of claim 9, whereinthe controller comprises a CMOS controller and wherein the CMOScontroller is configured to adjust the bias voltage based on atemperature measured in proximity to the CMOS controller.
 15. The poweramplification circuit of claim 9, wherein the impedance modulator isprovided as part of a pre-distortion circuit that corrects amplitudemodulation to phase modulation (AMPM) distortion by distorting phase atthe input terminal in a direction opposite to original distortionprovided by an input signal received at the input terminal.
 16. Acircuit, comprising: a detecting amplifier that receives a signal outputby a drive amplifier and that amplifies the signal output by the driveamplifier; an inverting amplifier that receives an output of thedetecting amplifier and that modulates the output of the detectingamplifier; and a capacitor having a capacitance that is adjustedinversely relative to the signal output by the drive amplifier, whereinthe capacitor is shunt connected to an input of the drive amplifier. 17.The circuit of claim 16, further comprising: a main stage amplifierhaving an input connected to an output of the drive amplifier and havingan output connected to an output terminal; and a CMOS controllerconfigured to control a bias voltage provided between the invertingamplifier and the detecting amplifier based on a frequency at whichinput signals are received at the input of the drive amplifier.
 18. Thecircuit of claim 16, wherein an output of the inverting amplifier isprovided to the capacitor.
 19. The circuit of claim 18, furthercomprising: a switch connected between the capacitor and the invertingamplifier and that selectively enables or disables current from flowingbetween the capacitor and the inverting amplifier.
 20. The circuit ofclaim 16, further comprising a resistor connected between ground and anoutput of the inverting amplifier.